Role of phosphoinositide 3-kinase p110δ in TLR4- and TLR9-mediated B cell cytokine production and differentiation

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Phosphoinositide 3-kinase (PI3K) enzymes play key roles in signaling via antigen receptors and cytokine receptors and isoform-selective PI3K inhibitors are being evaluated as targets for treatment of allergic and inflammatory diseases. The specific roles of PI3K isoforms in TLR-mediated activation of lymphocytes have not been defined. In this study we assess the role of p110δ PI3K in TLR4, TLR9, or TLR4 + TLR9-mediated B cell responses. Utilizing both p110δ-mutant mice and p110δ-specific inhibitor IC87114, we find that signaling via p110δ is required for optimal B cell proliferation, but is not required for TLR-mediated B cell differentiation into plasma cells or Ig isotype switch. However PI3K blockade led to increased frequencies of IgG1 and IgE expressing cells, and partially reversed ability of CpG to inhibit IgG1 and IgE. Examination of B cell cytokine production revealed that p110δ blockade markedly reduced IL-6 and IL-10 production. In contrast, p110δ signaling was clearly not required for IL-12 production, with p110δ-mutant B cells in fact showing enhanced IL-12 p70 production. TLR4– and TLR9–ligands act in synergy to drive IL-6 and IL-10 production, but not IL-12, and this additive effect is independent of p110δ signaling. Together, these results indicate that PI3Kδ functions in influencing the type of B cell cytokine production and differentiation response induced by TLR–ligands.

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